outboard in well inside boat

Discussion in 'Boat Design' started by orb353, May 31, 2012.

  1. orb353
    Joined: Feb 2010
    Posts: 25
    Likes: 2, Points: 0, Legacy Rep: 20
    Location: GA

    orb353 Junior Member

    I have a 26' center console boat that I am replacing the floor, transom and all wet foam in. I am also repowering the boat. It is a early 70's aquasport 240. Beam is 8', weight 3000 pounds with outboard. It has a slightly warped V. Deadrise at transom is 14 degrees. I have considered repowering with a 180- 220 hp diesel, jackshafted to an outdrive. But the costs out weigh the benefits of the diesel. I really do not use it enough to justify spending about 10K on a diesel.

    I want the improved handling that comes with the weight of the engine a little forward of the transom, and the point of thrust also slightly forward of the transom to avoid transom squat when accelerating, trying to get on a plane. Also, I would love to have the outboard off the transom. I am a diver, and having the engine out of the way would really come in handy.

    I think that putting the outboard in a well would add flotation to the transom, getting a better trim angle while running on a plane, and hold it on a plane at a low speed.

    Thus my idea of putting the outboard in a well, about 2' forward of the transom. I think I can create a well, with a smaller hole at the bottom, to put the outboard through, and create a two piece plate to attach from the bottom to eliminate water flow disruption, somewhat, and also allow it to turn. Basic Idea, to stick an an outboard out the bottom of the hull, like one of these new pod drives. The transom of the boat is high enough that a 20" motor will just come to the top of the transom cap, so the engine would not be sticking up really high. I do not care about tilting the engine, just being able to trim slightly. I considered making a tunnel and sticking it down in that, to eliminate draft.

    Like the aluminum boat with the outboard sticking out of the bottom. minus the keel. I thought of flattening the deadrise, , but without the reverse deadrise on that boat, or making a tunnel like the boat in pic with pods. The flats skiffs have those floatation sponsons-pods on the back to help with flotation and stern squat, same basic principle I am trying to achieve.

    Will this work? Any ideas? Has anyone tried anything like this?

    Thanks
    Oliver Barratt
     

    Attached Files:

  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,156
    Likes: 958, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'm not 100% clear about your plan, it sounds as though you could get rid of the squat rising on to plane with trim tabs, though. That leaves just the issue of having the stern clear for easier boarding by divers, but surely installing platforms either side of the outboard could help out there ? Otherwise seems like a lot of bother for an uncertain result, if the well is closed on all sides you have to be careful about the back of it 'catching' the water flow. The only applications for such modifications I have seen were net fisherman who wanted to haul their nets over the stern without snagging on outboards, but you may have to do the occasional dive to clear anchor lines if they foul the prop, seeing it won't be tiltable. Don't forget that excising portion of the bottom will alter the way it performs underway, and it will steer differently as well. Not worth it, imo, you will create an orphan that will be unsaleable as well.
     
  3. thudpucker
    Joined: Jul 2007
    Posts: 885
    Likes: 31, Points: 0, Legacy Rep: 453
    Location: Al.

    thudpucker Senior Member

    I rode in a 21' Columbia Sail boat on the Columbia River with a 10 Hp Honda sticking down through a hole just fwd of the Rudder, and near the end of the keel.
    Worked pretty good I thought.
    The Hole wasn't big enough to bring the Outboard prop n' skeg up through. He had to pay a diver to take the prop off when he needed to pull the motor.
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,156
    Likes: 958, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I recall seeing a fisherman's net skiff about 20' with a V6 Johnson outboard right forward in a well, about where the forefoot turns. Can't imagine how that would have worked out, in a lot of ways, steering, aeration of the prop, you name it.
     
  5. philSweet
    Joined: May 2008
    Posts: 2,456
    Likes: 266, Points: 83, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Take it one step at a time. Once you've dug out 500# of soggy foam and replaced it with decent stuff she will handle fine. We had one in the Everglades that we used as a chase boat for broken down house boats. Ugly as sin but mechanically sound and very tolerant of abuse. They aren't real fast to begin with. The lighter you keep it the better it will go. Our engines were something of a cobble due to the tow duty so I can't help you out there much. I think it would behave darn strange if you put it in a well. The well is just about where you want the planing surface. I can't think of any planing craft with a 14ish degree vees that run a well. Get her back in shape and hang an outboard and see what happens. Um, isn't the fuel tank where the well would go? or is it far enough forward?
     
  6. orb353
    Joined: Feb 2010
    Posts: 25
    Likes: 2, Points: 0, Legacy Rep: 20
    Location: GA

    orb353 Junior Member

    I don't think that trim tabs fully handle that issue. I had another boat a few years ago, a 20' center console. We put a bracket on the transom, and hung a 175 outboard on it. It was very stern heavy after that. We installed trim tabs, and that did help hold the bow down when on a plane, but it really need some positive floatation around the bracket and outboard. A full floatation bracket would help, or a bracket that has floatation that extends alittle aft of the transom, kinda around the outboard, like the little flats skiff in my pic, in my earlier post.

    I think the outboard well is a cool idea, but as you pointed out, performance will be unpredictable, and once it is done there is no going back.

    I am considering adding a full floatation bracket, that extends all the way to the bottom of the hull, basically extending the planing surface of the hull. The boat has a hull transom, so I have to add a bracket to allow the outboard to tilt up. And extending the bracket a little aft on each side of the outboard, basically creating those sponson pods things, to help with floatation.
     
  7. orb353
    Joined: Feb 2010
    Posts: 25
    Likes: 2, Points: 0, Legacy Rep: 20
    Location: GA

    orb353 Junior Member

    This a picture that I edited in photoshop, added a bracket, with the floatation on each side of the outboard, as serving as a swim platform. It extends the hull about 36".
     

    Attached Files:

  8. orb353
    Joined: Feb 2010
    Posts: 25
    Likes: 2, Points: 0, Legacy Rep: 20
    Location: GA

    orb353 Junior Member

    Kinda like the euro style bracket on the contender, but with a full floatation swim platform---pod--sponson. Of course on the contender the bracket is part of the hull, not an add on bracket.

    And accomplishing something similar to the computer generated model in the other pic.
    I think if i decide to go with a four stroke, I will need the extra floatation.

    Any ideas on how this will effect performance? Has anyone done anything similar on a planning hull?
    I am shooting for a wot of 30 knots, cruise 25 knots.

    And the last picture is what I am trying to avoid.
     

    Attached Files:

  9. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    Seeing that you will be involved in a major project , why not make some cheap extensions , and see how they work .

    You will lose the flexibility that the power trim offers , and may want trim tabs .
     
  10. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 43, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    Works very well, called a mullet skiff down here and used for net handling

    Steve


     

    Attached Files:

  11. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,156
    Likes: 958, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    That is exactly the thing I had in mind, I can only assume it is mainly a smooth water conveyance, otherwise things could get interesting leaping about in waves. :p
     
  12. orb353
    Joined: Feb 2010
    Posts: 25
    Likes: 2, Points: 0, Legacy Rep: 20
    Location: GA

    orb353 Junior Member

    Thanks for all info and ideas. I think I am going to add a full floatation bracket to the boat, and hang an outboard on it. Then add trim tabs. That way I will still be able to use the trim of the motor to somewhat control the trim attitude of the hull. along with the trim tabs.
    I think Frank Smith said it accurately. Adding the sponson-pod things (or putting it in a well) that extend the planing surface to the side of the outboard will not allow the outboard to use the bow up trim, when it is needed. The boat would run more like an inboard, or any boat with the prop under the hull. But using trim tabs to extend the running surface will allow either for trim up or down.
    I am going to try to build something similar to the contender integrated bracket, maybe even with trim tabs built into the bracket.
     

    Attached Files:


  13. dskira

    dskira Previous Member

    The barnacle have tendency to stick to the water intake, the algae too and all sort of thing when the engine is at rest. It is reason why an outboard base must be tilted out of the water when not running. And it is one of the best thing of an outboard. If you put in a well and can't tilt it you negate the entire concept and advantage of an outboard
     
    1 person likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.